Underground cryogenic storage of liquefied gas



March 21, 1967 w. D. WATERMAN 3,39,$83

UNDERGROUND CRYOGENIC STORAGE OF LIQUEFIED GAS Filed Oct. 11/1965 3 Sheets-Sheet 1 lW/dd/fi fi Mi k/M4 INVENTOR.

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arch 21, 1957 w. D. WATERMAN 9 3 UNDERGROUND CRYOGENIG STORAGE OF LIQUEFIED GAS Filed Oct. 11, 1965 3 Sheets-Sheet 2 March 21, 19 6'? w. D. WATERMAN 3,39,383

UNDERGROUND CRYOGENIC STORAGE OF LIQUEFIED GAS Filed Oct. 11, 1965 5 Sheets-Sheet 5 Mil/5 fl MTFWfi/K/ INVENTOR.

United States Patent Ofifice 33%,833 Patented Mar. 21, 1967 3,309,883 UNDERGROUND CRYOGENIC STORAGE F LIQUEFIED GAS Willis D. Waterman, Salina, Kans., assignor to Halliburton Company, Duncan, Okla, a corporation of Delaware Filed (Bot. 11, 1965, Ser. No. 494,585 Claims. (Cl. 6245) This invention relates to storage of liquefied gas in large volumes. This invention will be described in connection with storage of liquefied natural gas (LNG) but it will be understood that this is by way of illustration only.

The rapid growth of the natural gas industry has created a need for storage of large volumes of gas near metropolitan and industrial areas to supply peak demands in winter. Liquefication of the gas for storage is highly desirable inasmuch as storage of the gas as a liquid occupies less than one-third of the volume required for other storage methods. Gas volumes equivalent to 630 s.c.f. can be stored in one cubic foot of storage space through liquefication of the gas. However, natural gas in the liquid state must be stored at a temperature of 260 F. at standard pressures and heretofore has required expensive, well insulated containers made from special steels.

The present invention contemplates refrigerated storage in frozen earth using a clustered cell arrangement in which the cells comprise closely spaced holes in the earth. Each storage cell within the cluster is designed to be selfsealing against leakage of the product and to be able to operate independently of any other cell. The self-sealing features are obtained by placing the storage volume of the cell entirely below the water-table of the earth formation so that any leak is automatically sealed through freezing of ground water by the very cold product.

Another aspect of the invention resides in a method and apparatus for constructing the storage cell and employing a liquid, for example drilling fluid, for preventing caving of the walls, freezing of the walls from the top down by introducing a refrigerant, applying a layer of buffer liquid between the refrigerant and the wall-sustaining drilling fluid, withdrawing drilling fluid from the bottom while adding refrigerant, and subsequently replacing the refrigerant with liquefied gas under pressure.

Another aspect of this invention relates to a vaporcondensing system within the borehole during the wallfreezing operation and also used during storage of liquefied gas. The vapor-condensing system employs a heat exchanger device at the surface as well as a pair of conduits communicating with the storage cell below a reinforced concrete cap forming the upper end of the storage space, one of the conduits communicating with the body of liquefied gas, the other communicating with vapor space above the body.

Other and more detailed objects and advantages will appear hereinafter.

In the drawings, FIGURE 1 is a schematic plan view of a cluster of storage cells employed in connection with this invention.

FIGURE 2 is a sectional elevation in schematic form showing construction of one of the cells and illustrating the method of freezing the walls of the storage space while supporting them against caving.

FIGURE 3 is a sectional view similar to FIGURE 2 showing the liquefied gas in place in the frozen storage chamber provided by the cell and showing operation of the vapor condensing system.

Referring to the drawings, the cluster of cells as shown in FIGURE 1 comprises a number of equally spaced cells 10 arranged in a generaly hexagonal pattern, each cell being formed by a borehole in the earth, the depth of each borehole being approximately the same as the overall size of the cluster to reduce the ratio of surface area to volume and thus minimize heat gains from the earth. The holes are drilled separately, and completed cells ready for storage of the product become available one by one. Thus at any one time there may be holes within the cluster which are being drilled, holes filled with drilling fluid, cells being frozen, cells holding refrigerant, and cells storing the vapor-phase product in liquid form at cryogenic temperatures.

More than one cryogenic product may be stored in the cluster (colder products should be stored in the center cells), and additional cells can be added to the cluster at any time additional storage capacity is needed. Moreover, the design of the storage cells permits them to operate at pressures above three atmospheres absolute,

to eliminate pumps, and to allow the product to be stored at higher temperatures with attendant reduced refrigeration costs. These refrigeration costs are further reduced in comparison with other types of storage because only relatively small areas of a limited number of holes are being frozen at any one time, and additional compressors for initially freezing the earth are not necessarily needed. Thus the refrigerating requirements for freezing the cells in series can be about the same as those needed for recondensing the boil-off from the completed cluster caused by heat gains from the earth.

These advantages and others relating to the safety of the stored liquefied gas and to efl'lcient operation accrue from the design of the cells within the cluster, the method and apparatus for freezing the walls of the boreholes, and the vapor-condensing system employed during the construction and later during the operation of the underground cryogenic storage.

As shown in FIGURE 2, construction of the cell 10 is begun by drilling an oversize hole 11 into the earth to a location several feet below the existing water-table. This hole 11 is lined with a steel casing 12 cemented in place by a layer of cement 13. A smaller borehole 14 is then drilled through the interior of the casing 12 into the earth formation to the finished depth. The drilling apparatus (not shown) is then moved to another cell location, leaving the borehole 14 and the casing 13 filled with a drilling fluid suited to the formations encountered to protect the hole from caving. The level of the drilling fluid in the hole is then lowered to the bottom of the casing 12. The vapor-condensing tray generally designated 15 is then attached to the base of the casing by straps 16. The construction and operation of this vapor-condensing tray are described in detail below. Piping assemblies 18 and 19 are installed in place, and a reinforced concrete cap 20 is poured near the bottom of the casing 12. The interior of the casing 12 above the concrete cap 20 is back-filled with wet earth 21. The borehole (now termed a cell) is now ready for freezing.

The method of freezing the walls of the borehole is practiced separately on each cell in the storage cluster.

An easily handled refrigerant such as propane is em-.

ployed. The earth walls of each cell are frozen from the inside and progressively from the top downwards for ease of construction and for early structural strength to the cap area of the cell. The freezing of the cell walls 14 is accomplished by first lowering the level of the drilling fiuid 21 several feet below the concrete cap 20 and then placing an insulating buffer liquid 22 on top of the drilling fluid 21. The bufier liquid should have a specific gravity greater than the refrigerant but less than water, he immiscible in both liquids, and have a low freezing point. There are several suitable buffer liquids of which caster oil and linseed oil are examples.

The refrigerant 23 is introduced into the cell through pipe 24 above the buffer liquid 22 and below the concrete cap 20. Drilling fluid 21 is removed through jacketed pipe 25 from below the buffer liquid 21 as refrigerant 23 is added, so that the frozen area of the cell wall 14 moves progressively downward at a rate controlled by the withdrawal of the drilling fluid 21. A valved outlet (not shown) on the surface controls flow of drilling fluid 21 through the jacketed pipe 25 under pressure of the refrigerant 23. The cell walls are restrained from caving because the internal pressure applied to the walls is essentially equivalent to that existing during the drilling of the borehole. In effect, cave-in dangers are minimized because the pressure of the drilling fluid against the cell walls 14 remains unchanged until the walls gain strength from freezing.

The vapor-condensing system is used both during the operation of freezing of the cell walls 14 and also during the subsequent storage of liquefied gas in the cell. The system includes the shallow annular aluminum tray 15 having a conical bottom wall joined to concentric inner and outer walls 31 and 32. The outer wall 32 is provided with an annular skirt 33 having its outer edge terminating close to the cell wall 14. The tray 15 has a plurality of V-shaped weirs 34 on the upper portion of the outer wall 32 and liquid within the tray overflows through these weirs and is directed by the skirt 33 against the cell walls 14. Surface equipment includes a transfer tank 35, a refrigerant circulating pump 36 and a heat exhcanger 37. This surface equipment may be used for a group of cells or for all cells in the cluster. Liquid refrigerant such as sub-cooled propane is circulated within the tray 15 and exchanged against a refrigerant of lower temperature in the heat exchanger 37. Subcooled propane stored in the transfer tank is introduced into the cell through the siphon pipe 39.

The vapor-condensing system is self-regulating within the conditions imposed by the desired wall-freezing rate and the rate of heat influx from the earth.

The operation of the vapor-condensing system depends upon the effects of changes in temperature, pressure and volume within the cell and interaction of components of the system in response to these changes. Basic adjustments of the system include regulation of the pressure in the transfer tank to control the pressure in the cell, and vertical changes in the vapor line 40 to change the refrigerant level in the tray 15. In turn, the change in refrigerant level varies the rate of spillover of refrigerant through the weirs 34. This overflow rate affects the level of the liquid in the cell and thus the heat exchange area between that liquid and the comically-shaped tray 15.

Interaction of the components for self-regulation of the system results from having refrigerant at similar pressures but dissimilar temperatures in the cell on the one hand and in the tray and transfer tank on the other, and from the action of siphon pipe 39 from the transfer tank 35 to the tray 15. This siphon pipe operates only when the refrigerant level in the tray falls below the lower end of the vapor line 40. Under normal construction conditions, the vapor line is adjusted to supply an amount of refrigerant from the transfer tank 35 that is equal to the amount of drilling fluid 21 removed from the cell, and heat exchange of the tray 15 removes the heat from the liquid in the cell that is gained from the earth. However, if the heat exchange is inadequate and the temperature of the liquid in the cell starts to rise, evaporation from the tray 15 increases, and the siphon pipe 39 withdraws refrigerants from the transfer tank 35 at a faster rate.

Heat influx from the earth is much reduced after the walls of the cell are frozen. At the time of completion of the freezing operation all of the drilling fluid 21 and buffer liquid 22 has been withdrawn from the cell through the jacketed pipe 25. The liquid level of the refrigerant is shown at 42 in FIGURE 2.

Placing of liquid natural gas (LNG) within the cell is then effected by displacing the liquid propane refrigerant with methane vapors and then adding LNG to the cell. There is no need for the nitrogen purge necessary to other types of cryogenic storage, and there is no contamination of the product. The level of the LNG in the cell need not remain near the tray 15 but may remain at any height 43 as shown in FIGURE 3 of the drawings. It should be noted that boiling of the liquid in the cell and in the tray 15 insures uniformly cold temperatures in the liquid column and affects superior heat transfer between the cold liquid and the earth walls 14. The operational costs of recondensing the boil-off are materially reduced if pressure is maintained on the cells, because of the lesser temperature differential between the stored product and the ground.

As shown in FIGURE 1, each of the cells 10 in the cluster is preferably provided with three separate piping connections 50, 51 and 52. The lines 50 are connected through sub-headers 53 and main-headers 54 to the fill and send-out line C. Similarly, the pipes 51 are connected through sub-headers 55 to main-headers 56 to the vapor return line B. Pipes 52 are connected through sub-headers 57 and main-headers 58 to the pressure maintenance line A. At each cell 10, pipe 50 is connected to the jacketed pipe 25, pipe 51 is connected to the vapor line 40 and pipe 52 is connected to the siphon pipe 39 through the transfer tank 35.

The following is given as an example of a typical clustered cell installation for storing a volume of 300,000 barrels of LNG (1,058,400 M s.c.f. of gas). Sixty-one cells would be used each with an effective volume of 4,925 barrels. The total depth of each borehole would be 179 /2 feet and the diameter of the cell 15 feet. The depth to the top of the concrete cap or plug would be 20 feet. The temperature of the stored liquid would be 258 F. An average boil-off of 0.3% of volume per day would be expected for the first year.

Clustered cell storage has unequaled safety because it is underground, it is self-sealing, and each cell is independent of the others in the cluster. Any damage that might occur does not affect the entire installation but is confined to a relatively small part of the storage cluster. This feature helps assure uninterrupted operation of the storage facility. Safety from leaks and the virtually certain consequent fires in the case of cryogenic hydrocarbons is important every where and is absolutely essential in metropolitan areas.

The clustered cell storage has great versatility of operation because any cryogenic product can be stored, because more than one product can be stored simultaneously in separate cells, and because additional storage cells may be added at any time.

Having fully described by invention, it is to be understood that I am not to be limited to the details herein set forth but that my invention is of the full scope of the appended claims.

I claim:

1. The method of constructing an underground storage cell for liquefied gas, comprising: forming a borehole in the earth, maintaining a drilling liquid in the borehole to prevent caving of the walls of the borehole, placing a layer of buffer liquid in the borehole above the drilling liquid, introducing refrigerant into the borehole above the buffer liquid while removing drilling liquid from the borehole below the buffer liquid, to cause the layer of buffer liquid to move progressively downward in the borehole, the buffer liquid having a specific gravity greater than the refrigerant and less than drilling fluid and being immiscible with both, whereby the earth wall of the borehole is frozen progressively downward by the refrigerant.

2. The method set forth in claim 1 including the step of installing a cap in the borehole, the refrigerant being introduced into the borehole below the cap and above the buffer liquid.

3. The method set forth in claim 1 including the steps of installing a casing in the upper portion of the borehole, placing a reinforced concrete cap in the casing, backfilling earth into the borehole above the cap, the refrigerant being introduced into the borehole below the cap and above the buffer liquid.

4. The method set forth in claim 1 in which the refrigerant is sub-cooled liquid propane.

5. The method of constructing an underground storage cell for liquefied natural gas, comprising: forming a borehole in the earth, maintaining a drilling liquid in the borehole to prevent caving of the walls of the borehole, installing a cap in the borehole, placing a layer of buffer liquid in the borehole above the drilling liquid, introducing subcooled propane into the borehole between the cap and the buffer liquid while removing drilling liquid from the borehole, the buffer liquid having a specific gravity greater than the propane and less than the drilling fluid and being immiscible with both, whereby the earth wall of the borehole is frozen progressively downward, employing methane vapor to displace the sub-cooled propane from the frozen borehole, and introducing liquefied natural gas into the borehole.

6. The method of freezing the walls of a borehole in the earth, the borehole containing a drilling liquid to prevent caving of the walls of the borehole, comprising: installing a cap in the borehole, installing a vapor-condensing tray in the borehole below the cap, removing drilling liquid from the borehole, placing a layer of buffer liquid in the borehole above the drilling liquid, introducing liquid refrigerant into the tray to overflow onto the walls of the borehole above the buffer liquid while removing drilling liquid from the borehole, the buffer liquid having a specific gravity greater than the drilling liquid and less than the refrigerant and being immiscible with both, whereby the earth wall of the unlined casing is frozen progressively downward.

7. An underground storage cell for liquefied gas, comprising: a borehole in the earth, a subsurface cap closing the borehole, a body of low-temperature liquefied gas under pressure in the borehole below the cap, a vapor-condensing tray in the borehole below the cap, the tray having means for directing liquid overflowing the tray into contact with the wall of the borehole, means forming a plurality of conduits extending through said cap, one of the conduits extending to the bottom of the borehole, and another communicating with vapor space above the tray.

8. The storage cell set forth in claim 7 in which the subsurface cap is formed of reinforced concrete, and in which the vapor condensing tray is annular and having inner and outer walls, the outer wall being provided with weirs and having means for directing liquid overflowing the tray through said weirs into contact with the wall of the borehole.

9. An underground storage cell for liquefied gas, comprising: a borehole in the earth, a subsurface cap closing the borehole, a body of low-temperature liquefied gas under pressure in the borehole below the cap, a vapor-condensing tray in the borehole below the cap, the tray having inner and outer walls for holding a pool of liquid on the tray, means for directing liquid overflowing the tray into contact with the wall of the borehole, means forming a plurality of conduits extending through said cap, one of the conduits extending to the bottom of the borehole, and another conduit communicating with the pool of liquid on the tray.

10. An underground storage cell for liquefied gas, comprising: a borehole in the earth, a subsurface cap closing the borehole, a body of low-temperature liquefied gas under pressure in the borehole below the cap, a vaporcondensing tray in the borehole below the cap and adapted to contain a pool of liquid, means forming a plurality of conduits extending through said cap, one of the conduits extending to the bottom of the borehole, another conduit communicating with the surface of the pool of liquid on the tray, and a third conduit communicating with the pool of liquid below its surface.

References Cited by the Examiner UNITED STATES PATENTS 2,787,455 4/1957 Knappen 61.5 2,796,739 6/ 1957 Meade et al. 6245 2,880,593 4/ 1959 Johnson et al. 6245 2,932,170 4/1960 Patterson et al. 6245 X 2,961,840 11/ 1960 Goldtrap 6245 2,994,200 8/ 1961 Carpenter 61.5 3,108,438 10/1963 Harvey 61.5 3,205,665 9/1965 Van Horn 6245 X LLOYD L. KING, Primary Examiner. 

1. THE METHOD OF CONSTRUCTING AN UNDERGROUND STORAGE CELL FOR LIQUEFIED GAS, COMPRISING: FORMING A BOREHOLD IN THE EARTH, MAINTAINING A DRILLING LIQUID IN THE BOREHOLE TO PREVENT CAVING OF THE WALLS OF THE BOREHOLE, PLACING A LAYER OF BUFFER LIQUID IN THE BOREHOLE ABOVE THE DRILLING LIQUID, INTRODUCING REFRIGERANT INTO THE BOREHOLE ABOVE THE BUFFER LIQUID WHILE REMOVING DRILLING LIQUID FROM THE BOREHOLE BELOW THE BUFFER LIQUID, TO CAUSE THE LAYER OF BUFFER LIQUID TO MOVE PROGRESSIVELY DOWNWARD IN THE BOREHOLE, THE BUFFER LIQUID HAVING A SPECIFIC GRAVITY GREATER THAN THE 